arXiv subjects

Jihyun Kim

Publications and source records attributed to Jihyun Kim.

40 records · Page 3Linked to original sources

arXiv2019

Filaments of Galaxies as a Clue to the Origin of Ultra-High-Energy Cosmic Rays

Ultra-high-energy cosmic rays (UHECRs) are known to come from outside of our Galaxy, but their origin still remains unknown. The Telescope Array (TA) experiment recently identified a high concentration in the arrival directions of UHECRs with energies above $5.7 \times 10^{19} eV$, called hotspot. We here report the presence of filaments of galaxies, connected to the Virgo Cluster, on the sky around the hotspot, and a statistically significant correlation between hotspot events and the filaments. With 5-year TA data, the maximum significance of binomial statistics for the correlation is estimated to be 6.1 $σ$ at correlation angle 3.4 degree. The probability that the above significance appears by chance is $\sim 2.0 \times 10^{-8}$ (5.6 $σ$). Based on this finding, we suggest a model for the origin of TA hotspot UHECRs; they are produced at sources in the Virgo Cluster, and escape to and propagate along filaments, before they are scattered toward us. This picture requires the filament magnetic fields of strength $\gtrsim 20$ nG, which need to be confirmed in future observations.

astro-ph.HE↗

arXiv2013

Revisit of Correlation Analysis between Active Galactic Nuclei and Ultra-High Energy Cosmic Rays

We update the previous analysis of correlation between ultra-high energy cosmic rays (UHECR) and active galactic nuclei (AGN), using 69 UHECR events with energy $E\ge55\,{\rm EeV}$ released in 2010 by Pierre Auger observatory and 862 AGN within the distance $d\le100\,{\rm Mpc}$ listed in the 13th edition of Véron-Cetty and Véron AGN catalog. To make the test hypothesis definite, we use the simple AGN source model in which UHECR are originated both from AGN, with the fraction $f_A$, and from the isotropic background. We treat all AGN as equal sources of UHECR, and introduce the smearing angle $θ_s$ to incorporate the effects of intervening magnetic fields. We compare the arrival direction distributions observed by PAO and expected from the model by the correlational angular distance distribution (CADD) method. CADD method rules out the AGN dominance model with a small smearing angle ($f_A\gtrsim0.7$ and $θ_s\lesssim6^\circ$). Concerning the isotropy, CADD shows that the distribution of PAO data is marginally consistent with isotropy. The best fit model lies around the AGN fraction $f_A=0.4$ and the moderate smearing angle $θ_s=10^\circ$. For the fiducial value $f_A=0.7$, the best probability of CADD was obtained at a rather large smearing angle $θ_{\rm s}=46^\circ$. Our results imply that for the whole AGN to be viable sources of UHECR, either an appreciable amount of additional isotropic background or the large smearing effect is required. Thus, we try to bin the distance range of AGN to narrow down the UHECR sources and found that the AGN residing in the distance range $60-80\,{\rm Mpc}$ have good correlation with the updated PAO data. It is an indication that further study on the subclass of AGN as the UHECR source may be quite interesting.

astro-ph.HE↗

arXiv2012

Correlation between Ultra-high Energy Cosmic Rays and Active Galactic Nuclei from Fermi Large Area Telescope

We study the possibility that the $γ$-ray loud active galactic nuclei (AGN) are the sources of ultra-high energy cosmic rays (UHECR), through the correlation analysis of their locations and the arrival directions of UHECR. We use the $γ$-ray loud AGN with $d\le 100 {\rm Mpc}$ from the second Fermi Large Area Telescope AGN catalog and the UHECR data with $E\ge 55 {\rm EeV}$ observed by Pierre Auger Observatory. The distribution of arrival directions expected from the $γ$-ray loud AGN is compared with that of the observed UHECR using the correlational angular distance distribution and the Kolmogorov-Smirnov test. We conclude that the hypothesis that the $γ$-ray loud AGN are the dominant sources of UHECR is disfavored unless there is a large smearing effect due to the intergalactic magnetic fields.

astro-ph.HE↗

arXiv2011

Statistical Analysis of the Correlation between Active Galactic Nuclei and Ultra-High Energy Cosmic Rays

We develop the statistical methods for comparing two sets of arrival directions of cosmic rays in which the two-dimensional distribution of arrival directions is reduced to the one-dimensional distributions so that the standard one-dimensional Kolmogorov-Smirnov test can be applied. Then we apply them to the analysis of correlation between the ultra-high energy cosmic rays (UHECR) with energies above $5.7\times10^{19}$ eV, observed by Pierre Auger Observatory (PAO) and Akeno Giant Air Shower Array (AGASA), and the active galactic nuclei (AGN) within the distance 100 Mpc. For statistical test, we set up the simple AGN model for UHECR sources in which a certain fraction of observed UHECR are originated from AGN within a chosen distance, assuming that all AGN have equal luminosity and smearing angle of UHECR, and the remaining fraction are from the isotropic background contribution. For the PAO data, our methods exclude not only a hypotheses that the observed UHECR are simply isotropically distributed but also a hypothesis that they are completely originated from the selected AGN. But, the addition of appropriate amount of isotropic component either through the background contribution or through the large smearing effect improves the correlation greatly and makes the AGN hypothesis for UHECR sources a viable one. We also point out that restricting AGN within the distance bin of 40-60 Mpc happens to yield a good correlation without appreciable isotropic component and large smearing effect. For the AGASA data, we don't find any significant correlation with AGN.

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